Process to prepare treprostinil, the active ingredient in Remodulin®

ABSTRACT

This present invention relates to an improved process to prepare prostacyclin derivatives. One embodiment provides for an improved process to convert benzindene triol to treprostinil via salts of treprostinil and to purify treprostinil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.14/849,981, filed Sep. 10, 2015, which is a Divisional of U.S.application Ser. No. 13/933,623, filed Jul. 2, 2013, which is aContinuation of U.S. application Ser. No. 13/548,446, filed Jul. 13,2012, which is a Continuation of U.S. application Ser. No. 12/334,731,filed Dec. 15, 2008, which claims priority from U.S. Provisional PatentApplication 61/014,232, filed Dec. 17, 2007, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

The present invention relates to a process for producing prostacyclinderivatives and novel intermediate compounds useful in the process.

Prostacyclin derivatives are useful pharmaceutical compounds possessingactivities such as platelet aggregation inhibition, gastric secretionreduction, lesion inhibition, and bronchodilation.

Treprostinil, the active ingredient in Remodulin®, was first describedin U.S. Pat. No. 4,306,075. Treprostinil, and other prostacyclinderivatives have been prepared as described in Moriarty, et al in J.Org. Chem. 2004, 69, 1890-1902, Drug of the Future, 2001, 26(4),364-374, U.S. Pat. Nos. 6,441,245, 6,528,688, 6,765,117 and 6,809,223.Their teachings are incorporated by reference to show how to practicethe embodiments of the present invention.

U.S. Pat. No. 5,153,222 describes use of treprostinil for treatment ofpulmonary hypertension. Treprostinil is approved for the intravenous aswell as subcutaneous route, the latter avoiding septic events associatedwith continuous intravenous catheters. U.S. Pat. Nos. 6,521,212 and6,756,033 describe administration of treprostinil by inhalation fortreatment of pulmonary hypertension, peripheral vascular disease andother diseases and conditions. U.S. Pat. No. 6,803,386 disclosesadministration of treprostinil for treating cancer such as lung, liver,brain, pancreatic, kidney, prostate, breast, colon and head-neck cancer.U.S. patent application publication No. 2005/0165111 disclosestreprostinil treatment of ischemic lesions. U.S. Pat. No. 7,199,157discloses that treprostinil treatment improves kidney functions. U.S.patent application publication No. 2005/0282903 discloses treprostiniltreatment of neuropathic foot ulcers. U.S. application Ser. No.12/028,471 filed Feb. 8, 2008, discloses treprostinil treatment ofpulmonary fibrosis. U.S. Pat. No. 6,054,486 discloses treatment ofperipheral vascular disease with treprostinil. U.S. patent applicationSer. No. 11/873,645 filed Oct. 17, 2007 discloses combination therapiescomprising treprostinil. U.S. publication No. 2008/0200449 disclosesdelivery of treprostinil using a metered dose inhaler. U.S. publicationNo. 2008/0280986 discloses treatment of interstitial lung disease withtreprostinil. U.S. application Ser. No. 12/028,471 filed Feb. 8, 2008discloses treatment of asthma with treprostinil. U.S. Pat. Nos.7,417,070, 7,384,978 and U.S. publication Nos. 2007/0078095,2005/0282901, and 2008/0249167 describe oral formulations oftreprostinil and other prostacyclin analogs.

Because Treprostinil, and other prostacyclin derivatives are of greatimportance from a medicinal point of view, a need exists for anefficient process to synthesize these compounds on a large scalesuitable for commercial production.

SUMMARY

The present invention provides in one embodiment a process for thepreparation of a compound of formula I, hydrate, solvate, prodrug, orpharmaceutically acceptable salt thereof

The process comprises the following steps:

(a) alkylating a compound of structure II with an alkylating agent toproduce a compound of formula III,

wherein

-   -   w=1, 2, or 3;    -   Y₁ is trans-CH═CH—, cis-CH═CH—, —CH₂(CH₂)_(m)—, or —C≡C—; m is        1, 2, or 3;    -   R₇ is    -   (1) —C_(p)H_(2p)—CH₃, wherein p is an integer from 1 to 5,        inclusive,    -   (2) phenoxy optionally substituted by one, two or three chloro,        fluoro, trifluoromethyl, (C₁-C₃) alkyl, or (C₁-C₃)alkoxy, with        the proviso that not more than two substituents are other than        alkyl, with the proviso that R₇ is phenoxy or substituted        phenoxy, only when R₃ and R₄ are hydrogen or methyl, being the        same or different,    -   (3) phenyl, benzyl, phenylethyl, or phenylpropyl optionally        substituted on the aromatic ring by one, two or three chloro,        fluoro, trifluoromethyl, (C₁-C₃)alkyl, or (C₁-C₃)alkoxy, with        the proviso that not more than two substituents are other than        alkyl,    -   (4) cis-CH═CH—CH₂—CH₃,    -   (5) —(CH₂)₂—CH(OH)—CH₃, or    -   (6) —(CH₂)₃—CH═C(CH₃)₂;    -   wherein —C(L₁)-R₇ taken together is    -   (1) (C₄-C₇)cycloalkyl optionally substituted by 1 to 3        (C₁-C₅)alkyl;    -   (2) 2-(2-furyl)ethyl,    -   (3) 2-(3-thienyl)ethoxy, or    -   (4) 3-thienyloxymethyl;    -   M₁ is α-OH:β-R₅ or α-R₅:β-OH or α-OR₂:β-R₅ or α-R₅:β-OR₂,        wherein R₅ is hydrogen or methyl, R₂ is an alcohol protecting        group, and    -   L₁ is α-R₃:β-R₄, α-R₄:β-R₃, or a mixture of α-R₃:β-R₄ and        α-R₄:β-R₃, wherein R₃ and R₄ are hydrogen, methyl, or fluoro,        being the same or different, with the proviso that one of R₃ and        R₄ is fluoro only when the other is hydrogen or fluoro.

(b) hydrolyzing the product of step (a) with a base,

(c) contacting the product of step (b) with a base B to for a salt offormula I_(s)

(d) reacting the salt from step (c) with an acid to form the compound offormula I.

The present invention provides in another embodiment a process for thepreparation of a compound of formula IV.

The process comprises the following steps:

(a) alkylating a compound of structure V with an alkylating agent toproduce a compound of formula VI,

(b) hydrolyzing the product of step (a) with a base,

(c) contacting the product of step (b) with a base B to for a salt offormula IV_(s), and

(d) reacting the salt from step (b) with an acid to form the compound offormula IV.

DETAILED DESCRIPTION

The various terms used, separately and in combinations, in the processesherein described are defined below.

The expression “comprising” means “including but not limited to.” Thus,other non-mentioned substances, additives, carriers, or steps may bepresent. Unless otherwise specified, “a” or “an” means one or more.

C₁₋₃-alkyl is a straight or branched alkyl group containing 1-3 carbonatoms. Exemplary alkyl groups include methyl, ethyl, n-propyl, andisopropyl.

C₁₋₃-alkoxy is a straight or branched alkoxy group containing 1-3 carbonatoms. Exemplary alkoxy groups include methoxy, ethoxy, propoxy, andisopropoxy.

C₄₋₇-cycloalkyl is an optionally substituted monocyclic, bicyclic ortricyclic alkyl group containing between 4-7 carbon atoms. Exemplarycycloalkyl groups include but not limited to cyclobutyl, cyclopentyl,cyclohexyl, and cycloheptyl.

Combinations of substituents and variables envisioned by this inventionare only those that result in the formation of stable compounds. Theterm “stable”, as used herein, refers to compounds which possessstability sufficient to allow manufacture and which maintains theintegrity of the compound for a sufficient period of time to be usefulfor the purposes detailed herein.

As used herein, the term “prodrug” means a derivative of a compound thatcan hydrolyze, oxidize, or otherwise react under biological conditions(in vitro or in vivo) to provide an active compound. Examples ofprodrugs include, but are not limited to, derivatives of a compound thatinclude biohydrolyzable groups such as biohydrolyzable amides,biohydrolyzable esters, biohydrolyzable carbamates, biohydrolyzablecarbonates, biohydrolyzable ureides, and biohydrolyzable phosphateanalogues (e.g., monophosphate, diphosphate or triphosphate).

As used herein, “hydrate” is a form of a compound wherein watermolecules are combined in a certain ratio as an integral part of thestructure complex of the compound.

As used herein, “solvate” is a form of a compound where solventmolecules are combined in a certain ratio as an integral part of thestructure complex of the compound.

“Pharmaceutically acceptable” means in the present description beinguseful in preparing a pharmaceutical composition that is generally safe,non-toxic and neither biologically nor otherwise undesirable andincludes being useful for veterinary use as well as human pharmaceuticaluse.

“Pharmaceutically acceptable salts” mean salts which arepharmaceutically acceptable, as defined above, and which possess thedesired pharmacological activity. Such salts include acid addition saltsformed with organic and inorganic acids, such as hydrogen chloride,hydrogen bromide, hydrogen iodide, sulfuric acid, phosphoric acid,acetic acid, glycolic acid, maleic acid, malonic acid, oxalic acid,methanesulfonic acid, trifluoroacetic acid, fumaric acid, succinic acid,tartaric acid, citric acid, benzoic acid, ascorbic acid and the like.Base addition salts may be formed with organic and inorganic bases, suchas sodium, ammonia, potassium, calcium, ethanolamine, diethanolamine,N-methylglucamine, choline and the like. Included in the invention arepharmaceutically acceptable salts or compounds of any of the formulaeherein.

Depending on its structure, the phrase “pharmaceutically acceptablesalt,” as used herein, refers to a pharmaceutically acceptable organicor inorganic acid or base salt of a compound. Representativepharmaceutically acceptable salts include, e.g., alkali metal salts,alkali earth salts, ammonium salts, water-soluble and water-insolublesalts, such as the acetate, amsonate(4,4-diaminostilbene-2,2-disulfonate), benzenesulfonate, benzonate,bicarbonate, bisulfate, bitartrate, borate, bromide, butyrate, calcium,calcium edetate, camsylate, carbonate, chloride, citrate, clavulariate,dihydrochloride, edetate, edisylate, estolate, esylate, fumarate,gluceptate, gluconate, glutamate, glycollylarsanilate,hexafluorophosphate, hexylresorcinate, hydrabamine, hydrobromide,hydrochloride, hydroxynaphthoate, iodide, isothionate, lactate,lactobionate, laurate, malate, maleate, mandelate, mesylate,methylbromide, methylnitrate, methylsulfate, mucate, napsylate, nitrate,N-methylglucamine ammonium salt, 3-hydroxy-2-naphthoate, oleate,oxalate, palmitate, pamoate (1,1-methene-bis-2-hydroxy-3-naphthoate,einbonate), pantothenate, phosphate/diphosphate, picrate,polygalacturonate, propionate, p-toluenesulfonate, salicylate, stearate,subacetate, succinate, sulfate, sulfosalicylate, suramate, tannate,tartrate, teoclate, tosylate, triethiodide, and valerate salts.

The present invention provides for a process for producing treprostiniland other prostacyclin derivatives and novel intermediate compoundsuseful in the process. The process according to the present inventionprovides advantages on large-scale synthesis over the existing method.For example, the purification by column chromatography is eliminated,thus the required amount of flammable solvents and waste generated aregreatly reduced. Furthermore, the salt formation is a much easieroperation than column chromatography. Moreover, it was found that theproduct of the process according to the present invention has higherpurity. Therefore the present invention provides for a process that ismore economical, safer, faster, greener, easier to operate, and provideshigher purity.

One embodiment of the present invention is a process for the preparationof a compound of formula I, or a hydrate, solvate, prodrug, orpharmaceutically acceptable salt thereof

The process comprises the following steps:

(a) alkylating a compound of formula II with an alkylating agent toproduce a compound of formula III,

wherein

-   -   w=1, 2, or 3;    -   Y₁ is trans-CH═CH—, cis-CH═CH—, —CH₂(CH₂)_(m)—, or —C≡C—; m is        1, 2, or 3;    -   R₇ is    -   (1) —C_(p)H_(2p)—CH₃, wherein p is an integer from 1 to 5,        inclusive,    -   (2) phenoxy optionally substituted by one, two or three chloro,        fluoro, trifluoromethyl, (C₁-C₃) alkyl, or (C₁-C₃)alkoxy, with        the proviso that not more than two substituents are other than        alkyl, with the proviso that R₇ is phenoxy or substituted        phenoxy, only when R₃ and R₄ are hydrogen or methyl, being the        same or different,    -   (3) phenyl, benzyl, phenylethyl, or phenylpropyl optionally        substituted on the aromatic ring by one, two or three chloro,        fluoro, trifluoromethyl, (C₁-C₃)alkyl, or (C₁-C₃)alkoxy, with        the proviso that not more than two substituents are other than        alkyl,    -   (4) cis-CH═CH—CH₂—CH₃,    -   (5) —(CH₂)₂—CH(OH)—CH₃, or    -   (6) —(CH₂)₃—CH═C(CH₃)₂;    -   wherein —C(L₁)-R₇ taken together is    -   (1) (C₄-C₇)cycloalkyl optionally substituted by 1 to 3        (C₁-C₅)alkyl;    -   (2) 2-(2-furyl)ethyl,    -   (3) 2-(3-thienyl)ethoxy, or    -   (4) 3-thienyloxymethyl;    -   M₁ is α-OH:β-R₅ or α-R₅:β-OH or α-OR₂:β-R₅ or α-R₅:β-OR₂,        wherein R₅ is hydrogen or methyl, R₂ is an alcohol protecting        group, and    -   L₁ is α-R₃:β-R₄, α-R₄:β-R₃, or a mixture of α-R₃:β-R₄ and        α-R₄:β-R₃, wherein R₃ and R₄ are hydrogen, methyl, or fluoro,        being the same or different, with the proviso that one of R₃ and        R₄ is fluoro only when the other is hydrogen or fluoro.

(b) hydrolyzing the product of step (a) with a base,

(c) contacting the product of step (b) with a base B to for a salt offormula I_(s)

(d) reacting the salt from step (c) with an acid to form the compound offormula I.

In one embodiment, the compound of formula I is at least 90.0%, 95.0%,99.0%.

The compound of formula II can be prepared from a compound of formulaXI, which is a cyclization product of a compound of formula X asdescribed in U.S. Pat. No. 6,441,245.

Wherein n is 0, 1, 2, or 3.

The compound of formula II can be prepared alternatively from a compoundof formula XIII, which is a cyclization product of a compound of formulaXII as described in U.S. Pat. No. 6,700,025.

One embodiment of the present invention is a process for the preparationof a compound having formula IV, or a hydrate, solvate, orpharmaceutically acceptable salt thereof.

The process comprises

(a) alkylating a compound of structure V with an alkylating agent suchas ClCH₂CN to produce a compound of formula VI,

(b) hydrolyzing the product of step (a) with a base such as KOH,

(c) contacting the product of step (b) with a base B such asdiethanolamine to for a salt of the following structure, and

(d) reacting the salt from step (b) with an acid such as HCl to form thecompound of formula IV.

In one embodiment, the purity of compound of formula IV is at least90.0%, 95.0%, 99.0%, 99.5%.

In one embodiment, the process further comprises a step of isolating thesalt of formula IV_(s).

In one embodiment, the base B in step (c) may be ammonia,N-methylglucamine, procaine, tromethanine, magnesium, L-lysine,L-arginine, or triethanolamine.

The following abbreviations are used in the description and/or appendedclaims, and they have the following meanings:

“MW” means molecular weight.

“Eq.” means equivalent.

“TLC” means thin layer chromatography.

“HPLC” means high performance liquid chromatography.

“PMA” means phosphomolybdic acid.

“AUC” means area under curve.

In view of the foregoing considerations, and specific examples below,those who are skilled in the art will appreciate that how to selectnecessary reagents and solvents in practicing the present invention.

The invention will now be described in reference to the followingExamples. These examples are not to be regarded as limiting the scope ofthe present invention, but shall only serve in an illustrative manner.

EXAMPLES Example 1. Alkylation of Benzindene Triol

Name MW Amount Mol. Eq. Benzindene Triol 332.48 1250 g 3.76 1.00 K₂CO₃(powder) 138.20 1296 g 9.38 2.50 CICH₂CN  75.50 567 g 7.51 2.0  Bu₄NBr322.37 36 g 0.11 0.03 Acetone — 29 L — — Celite ®545 — 115 g — —

A 50-L, three-neck, round-bottom flask equipped with a mechanicalstirrer and a thermocouple was charged with benzindene triol (1250 g),acetone (19 L) and K₂CO₃ (powdered) (1296 g), chloroacetonitrile (567g), tetrabutylammonium bromide (36 g). The reaction mixture was stirredvigorously at room temperature (23±2° C.) for 16-72 h. The progress ofthe reaction was monitored by TLC. (methanol/CH₂Cl₂; 1:9 and developedby 10% ethanolic solution of PMA). After completion of reaction, thereaction mixture was filtered with/without Celite pad. The filter cakewas washed with acetone (10 L). The filtrate was concentrated in vacuoat 50-55° C. to give a light-brown, viscous liquid benzindene nitrile.The crude benzindene nitrile was used as such in the next step withoutfurther purification.

Example 2. Hydrolysis of Benzindene Nitrile

Name MW Amount Mol. Eq. Benzindene Nitrile 371.52 1397 g* 3.76 1.0 KOH56.11 844 g 15.04 4.0 Methanol — 12 L — — Water — 4.25 L — — *Note: Thisweight is based on 100% yield from the previous step. This is notisolated yield.

A 50-L, cylindrical reactor equipped with a heating/cooling system, amechanical stirrer, a condenser, and a thermocouple was charged with asolution of benzindene nitrile in methanol (12 L) and a solution of KOH(844 g of KOH dissolved in 4.25 L of water). The reaction mixture wasstirred and heated to reflux (temperature 72.2° C.). The progress of thereaction was monitored by TLC (for TLC purpose, 1-2 mL of reactionmixture was acidified with 3M HCl to pH 1-2 and extracted with ethylacetate. The ethyl acetate extract was used for TLC; Eluent:methanol/CH₂Cl₂; 1:9, and developed by 10% ethanolic solution of PMA).After completion of the reaction (˜5 h), the reaction mixture was cooledto −5 to 10° C. and quenched with a solution of hydrochloric acid (3M,3.1 L) while stirring. The reaction mixture was concentrated in vacuo at50-55° C. to obtain approximately 12-14 L of condensate. The condensatewas discarded.

The aqueous layer was diluted with water (7-8 L) and extracted withethyl acetate (2×6 L) to remove impurities soluble in ethyl acetate. Toaqueous layer, ethyl acetate (22 L) was added and the pH of reactionmixture was adjusted to 1-2 by adding 3M HCl (1.7 L) with stirring. Theorganic layer was separated and the aqueous layer was extracted withethyl acetate (2×11 L). The combined organic layers were washed withwater (3×10 L) and followed by washing with a solution of NaHCO₃ (30 gof NaHCO₃ dissolved in 12 L of water). The organic layer was furtherwashed with saturated solution of NaCl (3372 g of NaCl dissolved inwater (12 L)) and dried over anhydrous Na₂SO₄ (950-1000 g), oncefiltered.

The filtrate was transferred into a 72-L reactor equipped withmechanical stirrer, a condenser, and a thermocouple. To the solution oftreprostinil in reactor was added activated carbon (110-130 g). Thesuspension was heated to reflux (temperature 68-70° C.) for at least onehour. For filtration, a pad of Celite®545 (300-600 g) was prepared insintered glass funnel using ethyl acetate. The hot suspension wasfiltered through the pad of Celite®545. The Celite®545 was washed withethyl acetate until no compound was seen on TLC of the washings.

The filtrate (pale-yellow) was reduced to volume of 35-40 L byevaporation in vacuo at 50-55° C. for direct use in next step.

Example 3. Conversion of Treprostinil to Treprostinil DiethanolamineSalt (1:1)

Name MW Amount Mol Eq Treprostinil 390.52 1464 g* 3.75 1.0Diethanolamine 105.14 435 g 4.14 1.1 Ethanol — 5.1 L — — Ethyl acetate —35 L** — — Treprostinil Diethanolamine — 12 g — — Salt (seed) *Note:This weight is based on 100% yield from benzindene triol. It is notisolated yield. The treprostinil was carried from previous step in ethylacetate solution and used as such for this step. **Note: The totalvolume of ethyl acetate should be in range of 35-36 L (it should be 7times the volume of ethanol used). Approximately 35 L of ethyl acetatewas carried over from previous step and additional 1.0 L of ethylacetate was used for rinsing the flask.

A 50-L, cylindrical reactor equipped with a heating/cooling system, amechanical stirrer, a condenser, and a thermocouple was charged with asolution of treprostinil in ethyl acetate (35-40 L from the previousstep), anhydrous ethanol (5.1 L) and diethanolamine (435 g). Whilestirring, the reaction mixture was heated to 60-75° C., for 0.5-1.0 h toobtain a clear solution. The clear solution was cooled to 55±5° C. Atthis temperature, the seed of polymorph B of treprostinil diethanolaminesalt (˜12 g) was added to the clear solution. The suspension ofpolymorph B was stirred at this temperature for 1 h. The suspension wascooled to 20±2° C. overnight (over a period of 16-24 h). Thetreprostinil diethanolamine salt was collected by filtration usingAurora filter equipped with filter cloth, and the solid was washed withethyl acetate (2×8 L). The treprostinil diethanolamine salt wastransferred to a HDPE/glass container for air-drying in hood, followedby drying in a vacuum oven at 50±5° C. under high vacuum.

At this stage, if melting point of the treprostinil diethanolamine saltis more than 104° C., it was considered polymorph B. There is no need ofrecrystallization. If it is less than 104° C., it is recrystallized inEtOH-EtOAc to increase the melting point.

Data on Treprostinil Diethanolamine Salt (1:1)

Wt. of Wt. of Treprostinil Melting Batch Benzindene Diethanolamine SaltYield point No. Triol (g) (1:1) (g) (%) (° C.) 1 1250 1640 88.00104.3-106.3 2 1250 1528 82.00* 105.5-107.2 3 1250 1499 80.42**104.7-106.6 4 1236 1572 85.34 105-108 *Note: In this batch,approximately 1200 mL of ethyl acetate solution of treprostinil beforecarbon treatment was removed for R&D carbon treatment experiments.**Note: This batch was recrystallized, for this reason yield was lower.

Example 4. Heptane Slurry of Treprostinil Diethanolamine Salt (1:1)

Name Batch No. Amount Ratio Treprostinil 1 3168 g 1 Diethanolamine SaltHeptane — 37.5 L 12 Treprostinil 2 3071 g 1 Diethanolamine Salt Heptane— 36.0 L 12

A 50-L, cylindrical reactor equipped with a heating/cooling system, amechanical stirrer, a condenser, and a thermocouple was charged withslurry of treprostinil diethanolamine salt in heptane (35-40 L). Thesuspension was heated to 70-80° C. for 16-24 h. The suspension wascooled to 22±2° C. over a period of 1-2 h. The salt was collected byfiltration using Aurora filter. The cake was washed with heptane (15-30L) and the material was dried in Aurora filter for 1 h. The salt wastransferred to trays for air-drying overnight in hood until a constantweight of treprostinil diethanolamine salt was obtained. The materialwas dried in oven under high vacuum for 2-4 h at 50-55° C.

Analytical data on and Treprostinil Diethanolamine Salt (1:1)

Test Batch 1 Batch 2 IR Conforms Conforms Residue on Ignition (ROI)<0.1% w/w  <0.1% w/w Water content  0.1% w/w  0.0% w/w Melting point105.0-106.5° C. 104.5-105.5° C. Specific rotation [α]²⁵ ₅₈₉ +34.6° +35°Organic volatile impurities Ethanol Not detected Not detected Ethylacetate Not detected <0.05% w/w Heptane <0.05% w/w  <0.05% w/w HPLC(Assay) 100.4% 99.8% Diethanolamine Positive Positive

Example 5. Conversion of Treprostinil Diethanolamine Salt (1:1) toTreprostinil

A 250-mL, round-bottom flask equipped with magnetic stirrer was chargedwith treprostinil diethanolamine salt (4 g) and water (40 mL). Themixture was stirred to obtain a clear solution. To the clear solution,ethyl acetate (100 mL) was added. While stirring, 3M HCl (3.2 mL) wasadded slowly until pH ˜1 was attained. The mixture was stirred for 10minutes and organic layer was separated. The aqueous layer was extractedwith ethyl acetate (2×100 mL). The combined organic layers was washedwith water (2×100 mL), brine (1×50 mL) and dried over anhydrous Na₂SO₄.The ethyl acetate solution of treprostinil was filtered and the filtratewas concentrated under vacuum at 50° C. to give off-white solid. Thecrude treprostinil was recrystallized from 50% ethanol in water (70 mL).The pure treprostinil was collected in a Buchner funnel by filtrationand cake was washed with cold 20% ethanolic solution in water. The cakeof treprostinil was air-dried overnight and further dried in a vacuumoven at 50° C. under high vacuum to afford 2.9 g of treprostinil (Yield91.4%, purity (HPLC, AUC, 99.8%).

Analytical data on Treprostinil from Treprostinil Diethanolamine Salt(1:1) to Treprostinil

Batch No. Yield Purity (HPLC) 1 91.0% 99.8% (AUC) 2 92.0% 99.9% (AUC) 393.1% 99.7% (AUC) 4 93.3% 99.7% (AUC) 5 99.0% 99.8% (AUC) 6 94.6% 99.8%(AUC)

Example 6. Comparison of the Former Process and a Working Example of theProcess According to the Present Invention

Working example of the Process according to the Step Former Processpresent invention No. Steps (Batch size: 500 g) (Batch size: 5 kg)Nitrile 1 Triol weight 500 g 5,000 g 2 Acetone 20 L (1:40 wt/wt) 75 L(1:15 wt/wt) 3 Potassium 1,300 g (6.4 eq) 5,200 g (2.5 eq) carbonate 4Chloroacetonitrile 470 g (4.2 eq) 2,270 g (2 eq) 5 Tetrabutylammonium 42g (0.08 eq) 145 g (0.03 eq) bromide 6 Reactor size 72-Liter 50- gallon 7Reflux time 8 hours No heating, Room temperature (r.t.) 45 h 8 Hexanesaddition Yes (10 L) No before filtration 9 Filter Celite Celite 10Washing Ethyl acetate (10 L) Acetone (50 L) 11 Evaporation Yes Yes 12Purification Silica gel column No column Dichloromethane: 0.5 L Ethylacetate: 45 L Hexane: 60 L 13 Evaporation after Yes No column 14 Yieldof nitrite 109-112% Not checked Treprostinil (intermediate) 15 Methanol7.6 L (50-L reactor) 50 L (50-gal reactor) 16 Potassium 650 g (8 eq)3,375 g (4 eq) hydroxide 17 Water 2.2 L 17 L 18 % of KOH 30% 20% 19Reflux time 3-3.5 h 4-5 h 20 Acid used 2.6 L (3M) 12 L (3 M) 21 Removalof 3 × 3 L Ethyl acetate 2 × 20 L Ethyl acetate impurities 22Acidification 0.7 L 6.5 L 23 Ethyl acetate 5 × 17 L = 35 L 90 + 45 + 45= 180 L extraction 24 Water washing 2 × 8 L 3 × 40 L 25 Sodiumbicarbonate Not done 120 g in 30 L water + 15 L washing brine 26 Brinewashing Not done 1 × 40 L 27 Sodium sulfate 1 kg Not done 28 Sodiumsulfate Before charcoal, 6 L N/A filtration ethyl acetate 29 Charcoal170 g, reflux for 1.5 h, Pass hot solution (75° C.) filter over Celite,11 L through charcoal cartridge ethyl acetate and clean filter, 70 Lethyl acetate 30 Evaporation Yes, to get solid Yes, adjust to 150 Lintermediate treprostinil solution Treprostinil Diethanolamine Salt 31Salt formation Not done 1,744 g diethanolamine, 20 L ethanol at 60-75°C. 32 Cooling N/A To 20° C. over weekend; add 40 L ethyl acetate; cooledto 10° C. 33 Filtration N/A Wash with 70 L ethyl acetate 34 Drying N/AAir-dried to constant wt., 2 days Treprostinil (from 1.5 kg Treprostinildiethanolamine salt) 35 Hydrolysis N/A 15 L water + 25 L ethyl acetate +HCl 36 Extraction N/A 2 × 10 L ethyl acetate 37 Water wash N/A 3 × 10 L38 Brine wash N/A 1 × 10 L 39 Sodium sulfate N/A 1 kg, stir 40 FilterN/A Wash with 6 L ethyl acetate 41 Evaporation N/A To get solid,intermediate Treprostinil 42 Crude drying on tray 1 or 3 days Same 43Ethanol & water for 5.1 L + 5.1 L 10.2 L + 10.2 L (same %) cryst. 44Crystallization in 20-L rotavap flask 50-L jacketed reactor 45Temperature of 2 h r.t., fridge −0° C. 24 h 50° C. to 0° C. ramp, 0° C.crystallization overnight 46 Filtration Buchner funnel Aurora filter 47Washing 20% (10 L) cooled 20% (20 L) cooled ethanol-water ethanol-water48 Drying before oven Buchner funnel (20 h) Aurora filter (2.5 h) Tray(no) Tray (4 days) 49 Oven drying 15 hours, 55° C. 6-15 hours, 55° C. 50Vacuum <−0.095 mPA <5 Torr 51 UT-15 yield weight ~535 g ~1,100 g 52 %yield from triol) ~91% ~89% 53 Purity ~99.0%  99.9%

The quality of treprostinil produced according to this invention isexcellent. The purification of benzindene nitrile by columnchromatography is eliminated. The impurities carried over fromintermediate steps (i.e. alkylation of triol and hydrolysis ofbenzindene nitrile) are removed during the carbon treatment and the saltformation step. Additional advantages of this process are: (a) crudetreprostinil salts can be stored as raw material at ambient temperatureand can be converted to treprostinil by simple acidification withdiluted hydrochloric acid, and (b) the treprostinil salts can besynthesized from the solution of treprostinil without isolation. Thisprocess provides better quality of final product as well as savessignificant amount of solvents and manpower in purification ofintermediates.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the present invention is not so limited. It willoccur to those of ordinary skill in the art that various modificationsmay be made to the disclosed embodiments and that such modifications areintended to be within the scope of the present invention.

All of the publications, patent applications and patents cited in thisspecification are incorporated herein by reference in their entirety.

What is claimed is:
 1. A method of preparing a pharmaceutical batch of asalt of treprostinil that can be stored as a stable compound at ambienttemperature, said pharmaceutical batch being at least 2.9 grams, themethod comprising (a) alkylating a benzindene triol, (b) hydrolyzing theproduct of step (a) to form a solution comprising treprostinil, (c)contacting the solution comprising treprostinil from step (b) with abase to form a salt of treprostinil, wherein forming the salt of step(c) reduces the amount of one or more impurities resulting from steps(a) and/or (b) in the pharmaceutical batch.
 2. A method as claimed inclaim 1, wherein the salt of treprostinil is a diethanolamine salt.
 3. Amethod as claimed in claim 1, wherein no purification by columnchromatography is performed between steps (a) and (b).